(a) Field of the Invention
The present invention relates to a finder system for a camera and, more particularly, to a finder system for a single lens reflex camera using a group of plastic lenses for an eyepiece and a penta roof mirror.
(b) Description of the Related Art
A finder system for a single lens reflex camera generally requires a high quality view and high magnification. At the same time, in the non-professional camera market, cost reduction is also important.
In order to obtain a high magnification, a finder system uses a compact penta roof prism and reduces a focal length of an eyepiece. However, a shortened focal length of the eyepiece makes it difficult to compensate for aberrations such as astigmatism and distortion.
Plastic lenses may be used to lower manufacturing cost, but they cannot easily compensate for spherical aberration and distortion because they have a lower refractive index than that of glass which is generally used in an eyepiece.
A conventional single lens reflex camera uses a penta roof prism to provide an eyepiece with an image that is formed on the focusing screen when light passes through the camera's lens system and is reflected by the revolving reflective mirror. A penta roof prism in a single reflex camera inverts an image horizontally through the eyepiece. But the penta roof prism causes a camera to be heavy, which is against the current trend of compact and light-weight cameras.